Magnetic levitation apparatus

ABSTRACT

A magnetic levitation apparatus supports a magnetic element in a magnetic field. A control system controls a variable magnetic field to maintain the magnetic element at an equilibrium location relative to an unstable axis. In some embodiments the variable magnetic field has a gradient in the direction of the unstable axis but no field component. In some embodiments the magnetic field is provided by an array of four discrete magnets. In some embodiments additional magnets provide increased field intensity at the equilibrium location this increases stability of the levitated magnetic element against overturning. Light and electrical power may be supplied to the levitating magnetic element.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. patent application No.60/413,881 filed 27 Sep., 2002.

TECHNICAL FIELD

The invention relates to apparatus for levitating magnetic elements.

BACKGROUND

A levitated object is interesting to observe and can be useful invarious applications. Magnetic fields provide one tool which can be usedfor levitating magnetic objects. According to Earnshaw's theorem, it isnot possible to support a magnetic object in a stable manner using onlystatic magnetic fields. One statement of Earnshaw's theorem is that alevitated magnet cannot be held in stable equilibrium by any combinationof static magnetic or gravitational forces.

Whitehead, U.S. Pat. No. 5,168,183 discloses a magnetic levitationsystem in which an arrangement of magnets on one side of a separationplane can support a levitated magnetic element on an opposite side ofthe separation plane. The magnetic arrangement provides a staticmagnetic field such that, for displacements of the levitated element indirections parallel to a stability plane, the potential energy of themagnetic interaction between the levitated element and the staticmagnetic field increases. The magnetic arrangement includes a controlsystem which controls a variable force, which may be a variable magneticfield, to stabilize the levitated element in a direction perpendicularto the stability plane.

The inventors have determined that the magnetic fields generated by theembodiments disclosed by Whitehead tend to apply torque to levitatedmagnetic elements. This is because the magnetic dipole of the levitatedmagnetic element aligns generally with the static magnetic field whilethe variable magnetic field used to control the position of thelevitated magnetic element in the “unstable” direction is directedgenerally perpendicularly to the static magnetic field at theequilibrium location of the levitated magnetic element. The rotationcaused by this torque can lead to combined torsional and translationaloscillation of the levitated element. In some cases this adverselyaffects stable feedback control and thus the stability of the levitatedmagnetic element.

There is a need for magnetic levitation systems of the general typedisclosed by Whitehead which have desirable operating characteristics,such as increased stability of the levitated magnetic element, and/orare simple in construction. For certain applications, there is aparticular need for such levitation systems which incorporate a reducedamount of magnetic material and can be made at relatively low cost.

SUMMARY OF THE INVENTION

One aspect of the invention provides apparatus for levitating a magneticelement. The apparatus comprises at least two magnets arranged togenerate a static magnetic field providing a position-dependentpotential energy of interaction with a magnetic element. In certainembodiments the at least two magnets include four magnets arranged in adiamond pattern. The static magnetic field provides an equilibriumlocation wherein the potential energy decreases for displacements of themagnetic element away from the equilibrium location along an unstableaxis and increases for displacements of the magnetic element away fromthe equilibrium location in any direction perpendicular to the unstableaxis. The apparatus includes a position sensor generating a feedbacksignal indicative of the location of the magnetic element on theunstable axis, an electromagnet configured to generate a controlmagnetic field upon the passage of an electrical current through theelectromagnet, the control magnetic field having a gradient with respectto displacements along the unstable axis at the equilibrium location,and, a controller connected to receive the feedback signal and tocontrol the electrical current in the electromagnet to prevent themagnetic element from leaving a vicinity of the equilibrium location.

In some embodiments the electromagnet comprises at least two coilsspaced along an axis parallel to the unstable axis. For example, theelectromagnet may comprise four coils spaced along an axis parallel tothe unstable axis wherein upon the passage of the electrical currentthrough the four coils each of the four coils has a magnetic polarityopposite to the magnetic polarity of adjacent ones of the four coils.

A specific embodiment provides an apparatus wherein the at least twomagnets comprise first and second magnets spaced apart from one anotherby a first distance, D1, in a direction parallel to the unstable axisand third and fourth magnets spaced apart from one another by a seconddistance, D2, in a direction transverse to the unstable axis, whereinD1<D2, each of the first and second magnets is equidistant from an axisof symmetry of the at least two magnets and each of the third and fourthmagnets is equidistant from the axis of symmetry. Each of the first,second, third and fourth magnets may have a first magnetic pole facingtoward the equilibrium location and a second magnetic pole facing awayfrom the equilibrium location. The first magnetic poles of the first,second, third and fourth magnets may be substantially coplanar.

Another aspect of the invention provides apparatus for levitating amagnetic element. The apparatus comprises means for generating a staticmagnetic field providing a position-dependent potential energy ofinteraction with a magnetic element, the static magnetic field providingan equilibrium location wherein the potential energy decreases fordisplacements of the magnetic element away from the equilibrium locationalong an unstable axis and increases for displacements of the magneticelement away from the equilibrium location in any directionperpendicular to the unstable axis. The apparatus also comprises meansfor generating a feedback signal indicative of the location of themagnetic element on the unstable axis and control means for directingthe magnetic element to the equilibrium location by providing aquadrupole control magnetic field at the equilibrium location inresponse to the feedback signal.

Further aspects of the invention and features of specific embodiments ofthe invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate non-limiting embodiments of the invention,

FIG. 1 is a partially schematic view of a magnetic levitation systemaccording to one embodiment of the invention;

FIGS. 1A and 1B are partially schematic views of magnetic levitationsystems according to alternative embodiments of the invention.

FIGS. 2A through 2C are plots which show variation of magnetic potentialenergy with displacement from the equilibrium location of a levitatedmagnetic element along x, y and z axes of the system of FIG. 1respectively;

FIG. 3 is a top plan view of a magnetic levitation system having controlcoils arranged to generate a quadrupole field at a equilibrium location;

FIG. 4 is a top plan view of a magnetic levitation system having magnetsto improve stability of a levitated magnetic element against rotation;

FIG. 5 is a side view of a magnetic levitation system having a movableplatform for supporting a magnetic element near an equilibrium location;

FIG. 6 shows mechanisms for illuminating and animating a levitatedobject;

FIG. 7 is a section taken in the x-z plane through control coils of anembodiment of the invention; and,

FIGS. 8A and 8B show coil geometries according to alternativeembodiments of the invention.

DESCRIPTION

Throughout the following description, specific details are set forth inorder to provide a more thorough understanding of the invention.However, the invention may be practiced without these particulars. Inother instances, well known elements have not been shown or described indetail to avoid unnecessarily obscuring the invention. Accordingly, thespecification and drawings are to be regarded in an illustrative, ratherthan a restrictive, sense.

FIG. 1 shows a magnetic levitation system 10 according to the invention.System 10 is shown levitating a magnetic element 12 at an equilibriumlocation 13. Magnetic element 12 comprises a magnetic dipole or an arrayof magnetic dipoles. Magnetic element 12 may comprise a permanent magnetattached to a lightweight body to be levitated.

System 10 comprises a first pair of magnets 14 (individually 14A and14B) spaced apart by a distance D1 and a second pair of magnets 16(individually 16A and 16B) spaced apart by a distance D2 with D2>D1. Incurrently preferred embodiments of the invention, the ratio D2: D1 is inthe range of 1½:1 to 2:2.

Magnets 16, which are further apart than magnets 14, preferably havedipole moments larger than or equal to those of magnets 14. The magneticdipole moments of magnets 16 are preferably large enough tosubstantially counteract the undesirable curvature of the field lines ofthe magnetic field that would be present in the absence of magnets 16,but not so large as to counteract the levitating field of theless-powerful magnets 14, which has much higher gradients due to theproximity of magnets 14 to equilibrium location 13. Preferably magnets14A and 14B have the same magnetic strength as one another and magnets16A and 16B have the same magnetic strength as one another. Thestrength, M₁₄ of magnets 14 is preferably less than or equal to thestrength, M₁₆, of magnets 16. The ratio of M₁₆:M₁₄ is in the range of1:1 to 2:1 in some embodiments of the invention.

Magnets 14 are ideally arranged so that magnets 14A and 14B are disposeda first axis and magnets 16A and 16B are disposed on a second axisorthogonal to the first axis. In the following description, magnets 14and 16 are all shown as being adjacent a plane 18. A cartesiancoordinate system having orthogonal x and y axes in plane 18 and a zaxis normal to plane 18 has its origin located symmetrically relative tomagnets 14 and 16. The x axis extends through magnets 14 and they axisextends through magnets 16. The z axis of the coordinate system of theillustrated system 10 provides a symmetry axis of system 10. The z axisextends through equilibrium location 13, which is a distance D3 awayfrom plane 18.

While FIG. 1 shows the ideal case where magnets 14 and 16 are located onorthogonal axes, some deviation from this ideal arrangement is possiblewithout departing from the invention. In the illustrated embodiment,magnets 14 and 16 are arranged in a diamond pattern. The establishmentof a cartesian coordinate system is done only for convenience indescribing the configuration of the illustrated apparatus. Othercoordinate systems could be used.

Magnets 14 and 16 are preferably small in size compared to the distancesbetween magnets 14, 16 and equilibrium location 13 at which magneticelement 12 can be levitated by system 10. In his case, each of magnets14 and 16 produces a magnetic field at equilibrium location 13substantially the same as a field which would be produced by a singlemagnetic dipole at the location of the magnet 14 or 16.

In the embodiment illustrated in FIG. 1, magnets 14 and 16 are allpolarized in the same direction, which is parallel to the z axis. FIG.1A shows schematically an alternative embodiment of the inventionwherein each of magnets 14 are inclined toward the z axis at an angle,φ₁, and each of magnets 16 are inclined toward the z axis at an angle,φ₂. In some embodiments φ₁=φ₂. In other embodiments φ₁ and φ₂ aredifferent from one another. Inclining magnets 14 and/or 16 toward the zaxis, as shown in FIG. 1A tends to gain some “stiffness” in thelevitation of magnetic element 12 with respect to motion in onedirection at the expense of reduced stability in one or more otherdirections.

Magnets 14 and 16 have poles of a first polarity (for example, N)oriented in a first direction (for example, the +z direction) and polesof a second polarity (for example S) oriented in a second directionopposite to the first direction (for example, the −z direction).

Any suitable magnets may be used for magnets 14 and 16. Magnets 14 and16 may, for example, comprise permanent magnets or electromagnets. Wheresystem 10 is to be powered by batteries or another power supply that islimited in terms of total capacity or peak power, or in cases where itis desirable to minimize the electrical power consumption of system 10,magnets 14 and 16 are preferably permanent magnets. In some embodiments,magnets 14 and 16 comprise NdFeB, Barium Ferrite, Samarium Cobalt orAlNiCo magnets. Magnets 14 and 16 may each comprise an array of magneticdipoles.

In the illustrated embodiment, the poles of magnets 14 and 16 which areclosest to equilibrium location 13 are co-planar and all lie immediatelyadjacent to a plane 18. Magnets 14 and 16 may be mounted within a base17 (See FIGS. 1B, 5 and 6). Magnets 14, 16 and base 17 may be thin inthe z direction. In some embodiments base 17 has a thicknesssignificantly less than D3. For example, base 17 may have a thickness of½×D3 or less.

Magnets 14 and 16 generate a static magnetic field that supportsmagnetic element 12 in levitation at equilibrium location 13. The staticmagnetic field has gradients such that a potential energy of themagnetic interaction between levitated magnetic element 12 and thestatic magnetic field increases for small displacements of levitatedmagnetic element 12 from equilibrium location 13 in directions parallelto a stability plane 20 (illustrated as the y-z plane in FIG. 1).

FIGS. 2A, 2B and 2C illustrate the variation of magnetic potentialenergy with position of magnetic element 12 for displacements along x, yand z axes respectively. It can be seen that the magnetic potentialenergy increases for displacements away from equilibrium location 13along either of they and z axes. Magnetic element 12 is therefore stablein respect of displacements along these axes. On the other hand, themagnetic potential energy decreases for displacements away fromequilibrium location 13 in either direction along the x axis. Magneticelement 12 is therefore unstable in respect of displacements fromequilibrium location 13 along the x axis.

System 10 includes control coils 22 (individually 22A and 22B) whichgenerate a variable magnetic field under the control of a controller 24(FIG. 1). When magnetic element 12 moves away from its levitatedequilibrium position 13, controller 24 adjusts flow(s) of electricalcurrent in the control coils to cause control coils 22 to generate amagnetic field that results in a force being applied to magnetic element12. The force pushes magnetic element 12 in a selected direction alongthe unstable x axis. The variable magnetic field generated by thepassage of electrical current in the control coils stabilizes levitatedmagnetic element 12 with respect to motions in the direction of the xaxis. In the embodiment illustrated in FIG. 1, coils 22A, and 22B areadjacent to one another, have their centers spaced apart along the xaxis, and each of coils 22 surrounds one of magnets 14.

A position sensor 26 provides a signal representative of thedisplacement of levitated magnetic element 12 on the unstable x axis tocontroller 24. In the illustrated embodiment, sensor 26 is located atthe center of symmetry of system 10 directly below equilibrium location13. Position sensor 26 may comprise a Hall effect sensor, for example. AHall effect sensor may be oriented to detect the magnetic fieldintensity from levitated magnetic element 12 in a direction parallel tothe x axis. When magnetic element 12 is located at equilibrium location13 then the magnetic dipole of magnetic element 12 is aligned with thestatic magnetic field, which is oriented parallel to the z axis. Themagnetic dipole of magnetic element 12 yields no net magnetic fieldcomponent in a direction parallel to the x axis at the location ofsensor 26. If magnetic element 12 moves along the unstable x axis ineither direction then the field from its magnetic dipole, as detected atsensor 26, has a non-zero component in the x direction which increaseswith increasing displacement of magnetic element 12 from equilibriumlocation 13. Thus, the signal output by a Hall effect sensor 26 can beused to provide feedback to controller 24 regarding the position ofmagnetic element 12 along the unstable x axis.

Controller 24 adjusts current in coils 22 to maintain levitated magneticelement 12 at equilibrium location 13. Controller 24 may comprise anysuitable control technology including a suitably programmed dataprocessor such as a computer, programmable controller, or digital signalprocessor, or a suitable analog or digital feedback control circuit.

The distance D3 between equilibrium location 13 at which magneticelement 12 can be stably levitated and the plane 18 adjacent to magnets14 and 16 may be varied by adjusting distance D1 between magnets 14A and14B. Decreasing distance D1 slightly while magnetic element 12 is beinglevitated causes distance D3 to decrease while increasing the stabilityof magnetic element 12 with respect to displacements from equilibriumlocation 13 in stability plane 20 (i.e. the y-z plane in FIG. 1).Increasing distance D1 slightly while magnetic element 12 is beinglevitated causes distance D3 to increase while decreasing the stabilityof magnetic element 12 with respect to displacements from equilibriumlocation 13 in stability plane 20.

Preferably equilibrium location 13 is a position such that the staticmagnetic field of magnets 14 and 16 provides sufficient force tocounteract the force of gravity on magnetic element 12 at equilibriumlocation 13 in the absence of current flowing in coils 22. Magneticelement 12 is unstable in the x direction. Coils 22 are operated tocounteract any movement in the x direction of magnetic element 12 awayfrom equilibrium location 13. In such embodiments it is only necessaryto cause current to flow in coils 22 when magnetic element 12 has movedor is moving away from equilibrium location 13. This makes it possibleto minimize the electrical power expenditure required to stabilizemagnetic element 12 at equilibrium location 13.

Control coils 22 are arranged so that they can be operated to provide amagnetic field gradient (dBz/dx) near equilibrium location 13 sufficientto control the position of magnetic element 12 on the unstable x axis.The dimensions and locations of coils 22 may advantageously be chosen sothat the magnitude of the magnetic field produced by coils 22 is verysmall in the vicinity of equilibrium location 13. This permitsstabilization of magnetic element 12 without introducing significanttransverse magnetic field components at the location of magnetic element12 which would tend to rotate magnetic element 12. In practice, it isdesirable that the components of the magnetic field from coils 22 in thex, y and z directions be as small as practical at equilibrium location13 while having a gradient (dBz/dx) in the x direction large enough toprovide sufficient force to control the position of magnetic element 12on the x axis.

FIG. 3 illustrates a system 10A having one configuration of controlcoils 22 which minimizes the magnetic field from coils 22 in thevicinity of equilibrium location 13. The same reference numbers are usedto indicate parts of system 10A which are also found in system 10 ofFIG. 1. System 10A has four coils 22, coils 22A, 22B, 22C, and 22D.Coils 22A through 22D are rectangular coils arranged parallel to plane18 and parallel to one another. The long sides of coils 22A to 22Dextend parallel to the y axis and transversely to the unstable x axis.Coils 22A through 22D are arrayed symmetrically along the x axis.Magnets 14A and 14B may be within coils 22A and 22B respectively, asshown. Coils 22A through 22D are located symmetrically with respect tothe y-z stability plane. Ideally coils 22A and 22B are close together,coils 22A and 22C are close together and coils 22B and 22D are closetogether. Coils 22C and 22D are preferably wider than coils 22A and 22Bin their dimensions parallel to the x axis. In the illustratedembodiment, coil 22A has the same dimensions as coil 22B and coil 22Chas the same dimensions as coil 22D.

It is desirable that at least those components of the magnetic fieldsgenerated by coils 22 which are parallel to plane 18 substantiallycancel one another, at least in the vicinity of equilibrium location 13.This result may be produced by suitably choosing the dimensions of coils22 and passing appropriate electric current(s) through coils 22 inappropriate senses. Electrical current passes through inner coils 22Aand 22B in opposite senses to generate a stabilizing magnetic force onmagnet 12. If the current passes through coil 22A in a clockwise sense,current must pass counterclockwise through coil 22B. At the same time,the current flow in coil 22C is counterclockwise and the current flow incoil 22D is clockwise. This creates a stabilizing magnetic field whichapplies force to urge magnetic element 12 in one direction along theunstable x axis. To create a stabilizing magnetic field which appliesforce to urge magnetic element 12 in the opposite direction along theunstable x axis, the sense in which current flows in each of coils 22can be reversed.

The arrangement of coils 22 shown in FIG. 3 produces a magneticquadrupole field at equilibrium location 13 when coils 22 have equalnumbers of windings, suitable dimensions, and carry equal electricalcurrents flowing in the correct sense in each coil. A magneticquadrupole is a point in space where the magnitude of a magnetic fieldis zero while the gradients of the magnetic field are linear andsymmetric about the point. In this case, coils 22 cause a stabilizingmagnetic force to be applied to magnetic element 12. The magnitude ofthe stabilizing force applied to magnetic element 12 is proportional tothe magnitude of the gradient dBz/dx of the magnetic field at thelocation of magnetic element 12.

FIG. 7 is a section taken in the x-z plane through coils 22. For coils22 to produce a quadrupole field at equilibrium location 13 it isdesirable that coils 22A and 22B have equal widths W1, coils 22C and 22Dhave equal widths W2 and that W1 be related to W2 and the distance D3 byW1=D3 and W2≧D3. All of coils 22 may have the same length. The length ofeach coil 22 in the direction transverse to the unstable x axis isgreater than its width.

Controller 24 preferably inhibits the operation of system 10 in casemagnetic element 12 is not detected by sensor 26 as being in thevicinity of equilibrium location 13. For example, if magnetic element 12crashes it is desirable to prevent controller 24 from attempting tocorrect the position of magnetic element 12 by passing electricalcurrent through coils 22. This would waste energy, could cause coils 22to overheat, and in an extreme case could damage the control circuitswhich supply power to coils 22. Controller 24 may be configured toswitch to an inactive mode whenever the signal from sensor 26 indicatesthat magnetic element 12 is not within a desired distance of equilibriumlocation 13. Controller 24 may be configured to remain in the inactivemode until reset. System 10 may include a reset switch which can beoperated by a user to reset controller 24.

In some cases it can be desirable to provide additional magnets whichadd to the strength of the static magnetic field at equilibrium location13. The stability of magnetic element 12 against overturning momentsincreases with the strength of the static magnetic field at equilibriumlocation 13. This is because the magnetic dipole of magnetic element 12tends to align itself with the surrounding magnetic field. If themagnetic dipole of magnetic element 12 becomes misaligned with themagnetic field then magnetic element 12 experiences a corrective torque.The magnitude of the corrective torque is proportional to the strengthof the magnetic field at the location of magnetic element 12.

FIG. 4 shows an arrangement of additional magnets 30 which increases thestrength of the magnetic field at equilibrium location 13 but does notadversely affect the magnetic field gradients which create the forcesused to maintain magnetic element 12 at equilibrium location 13.Additional magnets 30 are arranged in a ring 31. Each additional magnet30 provides a magnetic dipole oriented in the same sense as magnets 14.

Ring 31 lies in plane 18 or in a plane parallel to plane 18. Equilibriumlocation 13 lies on a line extending perpendicular to the plane of ring31 from the center of ring 31. The radius of ring 31 is chosen so thatthe z component of the magnetic field produced by magnets 30 hassubstantially no gradient in the z direction at equilibrium location 13(i.e. at equilibrium location 13, dB(30)z/dz=0) where B(30)z is the zcomponent of the magnetic field produced by magnets 30. In this context,“substantially no gradient” means a gradient which is at leastsignificantly less than, preferably less than 25% of and most preferablyless than 7% of, the gradient of the static magnetic field produced bymagnets 14 and 16 which cause magnetic element 12 to levitate atequilibrium location 13. By virtue of symmetry of the magnets in ring 31about the z axis, there are no net horizontal components of the magneticfield produced by magnets 30 at equilibrium location 13 that would causemagnetic element 12 to align itself in any direction but parallel to thez axis.

System 10 may be started by initially supporting magnetic element 12 inthe vicinity of equilibrium location 13, engaging controller 24 and thenremoving whatever support is used to provide initial support to magneticelement 12. For example, system 10 may include a non-magnetic support 40which is movable relative to magnets 14 and 16 between a loweredposition 42A and a raised position 42B as shown in FIG. 5. When support40 is in its raised position 42B it supports magnetic element 12 atequilibrium location 13. After system 10 is operating to maintainmagnetic element 12 at equilibrium location 13, support 40 can belowered to position 42A.

Support 40 may comprise an arm, a table, a column, or the like. Support40 is movable between a first position in which it supports magneticelement 12 at or near equilibrium location 13 and a second position inwhich it is out of the way of equilibrium location 13. Any suitablemechanism may be provided to enable support 40 to move between the firstand second positions. The mechanism may comprise, for example, one ormore hinges, pivots, sliding members, flexible members, or the like.

As shown in FIG. 1B, system 10 may optionally include one or moresecondary electromagnets 22′. Secondary electromagnets 22′ may be usedto further stabilize magnetic element 12. For instance, an electromagnetthat is symmetric about the z axis and is located parallel to plane 18can generate a magnetic field gradient parallel to the z axis thataugments the static magnetic field from magnets 14 and 16. This magneticfield gradient will generate a force on the magnetic element 12 in adirection parallel to the z axis. The magnitude and sense of the forceis controlled by the electric current flowing in secondary electromagnet22′. A secondary sensor 26B oriented to detect motion of the magneticelement along the z axis provides feedback to a secondary controller 24B(which could be an independent control pathway provided by the samehardware/software used to provide controller 24 or could be a separateindependent controller). Controller 24B controls the electric currentflow in secondary electromagnet 22′. The secondary electromagnet systemmay be used to dampen vibration of magnetic element 12 along the z axisor to cause magnetic element 12 to move in the +z or −z direction aboutequilibrium location 13. By repeatedly reversing the flow of current insecondary electromagnet 22′ at an appropriate rate, controller 24B cancause magnetic element 12 to oscillate about equilibrium location 13along the z axis.

Electromagnets in other orientations with appropriate feedback sensorsmay be provided in conjunction with suitable controllers to provideforces on the magnetic element 12 along they axis or to provide magnetictorques on magnetic element 12. In this manner, the levitated elementcan be steered around the equilibrium location to a limited degree ormade to vibrate in some direction.

System 10 may include mechanisms to animate or illuminate magneticelement 12. FIG. 6 shows a novelty toy 50, which includes a mechanismfor animating magnetic element 12, and a system for illuminatingmagnetic element 12. FIG. 6 omits details of the mechanism forlevitating magnetic element 12 for clarity. The levitation mechanism maybe enclosed within base 17.

In toy 50, magnetic element 12 comprises a lightweight shell 52resembling the body of a helicopter. A permanent magnet 54 is affixedwithin shell 52. Magnet 54 interacts with a levitation system, asdescribed above, to levitate magnetic element 12 at an equilibriumlocation. Toy 50 includes an animation mechanism 60. Animation mechanism60 comprises a small electric motor 62 which drives a rotor 56. Motor 62is powered by electrical power supplied by way of a high frequencycoupling system. The coupling system may comprise an air coretransformer. A transmitting coil 66 mounted in base 17 is excited withhigh frequency (e.g. radio frequency) electrical signals. A signalemitted by transmitting coil 66 is coupled to a receiving coil 67 inmagnetic element 12. This induces electrical currents in receiving coil67. The electrical currents are rectified by a rectifier circuit 68 toproduce electricity which drives motor 62. Electricity from rectifiercircuit 68 could be used to power electrical devices other than or inaddition to motor 62. For example, the electricity could be used tooperate small lamps (which could be, for example, light-emitting diodes(LEDs).

Toy 50 also includes an illumination system 70. Illumination system 70comprises a high intensity light source 72 in base 17. Light source 72generates a beam 73 of light. Beam 73 illuminates a light receptor 74 onmagnetic element 12. In the illustrated embodiment, light receptor 74comprises a lens 75 which focuses light from beam 73 into a bundle ofoptical fibers 76. Optical fibers 76 extend to locations on shell 52corresponding to navigation lights and the like. Beam 73 may be tightlyconfined so that it is not readily apparent to a person observing toy50. Mirrors, diffusers or other optical elements may be used to directlight from light receptor 74 to illuminate surface features of magneticelement 12 instead of or in addition to optical fibers 76.

Where a component (e.g. a magnet, assembly, device, circuit, etc.) isreferred to above, unless otherwise indicated, reference to thatcomponent (including a reference to a “means”) should be interpreted asincluding as equivalents of that component any component which performsthe function of the described component (i.e., that is functionallyequivalent), including components which are not structurally equivalentto the disclosed structure which performs the function in theillustrated exemplary embodiments of the invention.

As will be apparent to those skilled in the art in the light of theforegoing disclosure, many alterations and modifications are possible inthe practice of this invention without departing from the spirit orscope thereof. For example:

-   -   In the illustrated embodiments, the magnetic dipole moments of        magnets 14 and 16 are parallel to one another. In some        embodiments of the invention, magnets 14 and/or 16 are oriented        so that their magnetic dipole moments lie at acute angles to        plane 18.    -   In the illustrated embodiment, the uppermost poles of magnets 14        and 16 are co-planar and all lie adjacent to a plane 18. Magnets        14 and 16 are not necessarily co-planar.    -   In the illustrated embodiments, the “N” poles of magnets 14 and        16 face equilibrium location 13. The polarity of magnets 14 and        16 could be reversed so that “S” poles of magnets 14 and 16 face        equilibrium location 13.    -   Control coils 22 are not necessarily formed of a plurality of        discrete coils. A single winding may be arranged to provide a        magnetic field substantially the same as the magnetic field        provided by a number of discrete coils.    -   Additional rings of magnetic dipoles concentric with ring 31 may        be provided. Since it is preferred that the ring (s) produce a        magnetic field for which dB(30)z/dz=0 at equilibrium location        13, where there are rings of different diameters, each ring is        preferably located at a different distance from equilibrium        location 13 to keep dB(30)z/dz=0.    -   Ring 31 may comprise one or more ring magnets instead of        discrete dipoles.    -   Magnets 14 and/or magnets 16 could be replaced by an arrangement        of symmetrically arranged smaller magnets which produce a        similar magnetic field. However, it is generally desirable to        use fewer discrete magnets, rather than more so as to minimize        the space taken up by magnets.    -   While coils 22 have been illustrated as being rectangular, other        coil shapes could also be used to generate a stabilizing        magnetic force on magnetic element 12. For example, the coils        could be triangular like coils 22E and 22F of FIG. 8A or        semicircular like coils 22G and 22H of FIG. 8B.    -   Any suitable non-contact sensor may be used for sensor 26.        Sensor 26 could, for example, comprise a suitable optical,        capacitative, or other sensor. Sensor 26 may detect the position        of magnetic element 12 along the unstable axis in any suitable        manner. In preferred embodiments, sensor 26 is of a type that        can detect motion of magnetic element 12 along the unstable axis        from a location that is removed from equilibrium location 13 by        a distance equal to the distance between plane 18 and        equilibrium location 13.

Accordingly, the scope of the invention is to be construed in accordancewith the substance defined by the following claims.

1. Apparatus for levitating a magnetic element, the apparatuscomprising: at least two magnets arranged to generate a static magneticfield providing a position-dependent potential energy of interactionwith a magnetic element, the static magnetic field providing anequilibrium location wherein the potential energy decreases fordisplacements of the magnetic element away from the equilibrium locationalong an unstable axis and increases for displacements of the magneticelement away from the equilibrium location in any directionperpendicular to the unstable axis; a position sensor generating afeedback signal indicative of the location of the magnetic element onthe unstable axis; an electromagnet configured to generate a controlmagnetic field upon the passage of an electrical current through theelectromagnet, the control magnetic field having a gradient with respectto displacements along the unstable axis at the equilibrium location;and a controller connected to receive the feedback signal and to controlthe electrical current in the electromagnet to prevent the magneticelement from leaving a vicinity of the equilibrium location.
 2. Anapparatus according to claim 1 wherein the electromagnet comprises atleast two coils spaced along an axis parallel to the unstable axis. 3.An apparatus according to claim 2 wherein the at least two coils arerectangular coils having long sides extending transversely to theunstable axis.
 4. An apparatus according to claim 2 wherein theelectromagnet comprises four coils spaced along an axis parallel to theunstable axis wherein upon the passage of the electrical current throughthe four coils each of the four coils has a magnetic polarity oppositeto the magnetic polarity of adjacent ones of the four coils.
 5. Anapparatus according to claim 2 wherein the electromagnet comprises fourcoils spaced along an axis parallel to the unstable axis, the four coilscomprising first and second rectangular coils located between third andfourth rectangular coils wherein, upon the passage of the electricalcurrent through the first through fourth coils, a component of amagnetic field produced by the first and second coils at the equilibriumlocation is cancelled by a magnetic field produced by the third andfourth coils.
 6. An apparatus according to claim 2 wherein the coils ofthe electromagnet are substantially coplanar.
 7. An apparatus accordingto claim 1 wherein the electromagnet is configured to generate aquadrupole magnetic field at the equilibrium location upon the passageof the electrical current.
 8. An apparatus according to claim 1 whereinthe at least two magnets comprise first, second, third and fourthmagnets arranged in a diamond pattern with me first and second magnetscloser together than the third and fourth magnets.
 9. An apparatusaccording to claim 8 wherein the third and fourth magnets are strongerthan the first and second magnets.
 10. An apparatus according to claim 1wherein the at least two magnets comprise first and second magnetsspaced apart from one another by a first distance, D1, in a directionparallel to the unstable axis and third and fourth magnets spaced apartfrom one another by a second distance, D2, in a direction transverse tothe unstable axis, wherein D1<D2, each of the first and second magnetsis equidistant from an axis of symmetry of the at least two magnets andeach of the third and fourth magnets is equidistant from the axis ofsymmetry.
 11. An apparatus according to claim 10 wherein each of thefirst and second magnets is equidistant from each of the third andfourth magnets.
 12. An apparatus according to claim 10 wherein each ofthe first, second, third and fourth magnets has a first magnetic polefacing toward the equilibrium location and a second magnetic pole facingaway from the equilibrium location and the first magnetic poles of thefirst, second, third and fourth magnets are substantially coplanar. 13.An apparatus according to claim 12 wherein the first magnetic poles ofthe first, second, third and fourth magnets are substantially coplanaradjacent to a plane extending perpendicular to the symmetry axis.
 14. Anapparatus according to claim 13 wherein the electromagnet comprises atleast two coils lying parallel to and adjacent the plane.
 15. Anapparatus according to claim 1 wherein the at least two magnets comprisepermanent magnets.
 16. An apparatus according to claim 1 wherein the atleast two magnets are all permanent magnets.
 17. An apparatus accordingto claim 10 wherein the electromagnet comprises at least two coilsspaced along an axis parallel to the unstable axis and a first one ofthe at least two coils extends around the first magnet and a second oneof the at least two coils extends around the second magnet.
 18. Anapparatus according to claim 17 where the at least two coils of theelectromagnet each have a width W1 along the axis parallel to theunstable axis equal to an equilibrium height D3, wherein the equilibriumheight D3 is a distance between the equilibrium position and a planepassing through the at least two coils.
 19. (cancel)
 19. An apparatusaccording to claim 18 comprising third and fourth coils positioned alongthe axis parallel to the unstable axis on either side of and adjacent tothe first and second coils, the third and fourth coils having havewidths W2 at least equal to width W1 of the first and second coils. 20.An apparatus according to claim 17 wherein the third and fourthpermanent magnets are both located outside of any of the at least twocoils.
 21. An apparatus according to claim 17 wherein the at least twocoils comprise rectangular coils.
 22. An apparatus according to claim 17wherein the at least two coils comprise semi-circular coils.
 23. Anapparatus according to claim 17 wherein the at least two coils comprisetriangular coils.
 24. An apparatus according to claim 12 wherein thefirst, second, third and fourth magnets are positioned such that a linepassing through the first and second magnetic poles of each of thefirst, second, third and fourth magnets intersects and forms an acuteangle with the axis of symmetry.
 25. An apparatus according to claim 8wherein the first, second, third and fourth permanent magnets arepermanent magnets selected from the group consisting of NdFeB, BariumFerrite, Samarium Cobalt and AlNiCo magnets.
 26. An apparatus accordingto claim 1 comprising an arrangement of field reinforcing magnetspositioned to generate a magnetic field which has substantially nogradient at the equilibrium location and which augments the staticmagnetic field near the equilibrium position.
 27. An apparatus accordingto claim 26 wherein the arrangement of field reinforcing magnetscomprises at least three magnetic dipoles spaced apart to form a ring.28. An apparatus according to claim 27 wherein the at least threemagnetic dipoles comprise at least three permanent magnets spaced apartto form the ring.
 29. An apparatus according to claim 27 wherein thearrangement of field reinforcing magnets comprises a secondaryelectromagnet.
 30. An apparatus according to claim 29 comprising asecondary controller for controlling an electrical current through thesecondary electromagnet and a secondary sensor for generating a feedbacksignal indicative of a distance of the magnetic element from a planepassing through the secondary electromagnet.
 31. An apparatus accordingto claim 1 comprising a transmitting coil connected to a source ofalternating current having a frequency in excess of 10 kHz wherein themagnetic element comprises a receiving coil and an electrical devicepowered by electrical current induced in the receiving coil.
 32. Anapparatus according to claim 31 wherein the electrical device comprisesa rectifier connected to supply direct current to a motor.
 33. Anapparatus according to claim 31 wherein the electrical device comprisesa lamp.
 34. An apparatus according to claim 1 comprising a light sourceoriented to direct a beam of light at a light receptor on the magneticelement wherein the magnetic element comprises an optical system fordirecting light from the light receptor to one or more visible locationson the magnetic element.
 35. An application according claim 1 comprisinga support moveable between an first position in which the supportsupports the magnetic element approximately at the equilibrium location,and a second position in which the support is out of the way of theequilibrium location.
 36. An apparatus according to claim 1 comprising asecondary electromagnet disposed to apply a force to the levitatedmagnetic element.
 37. Apparatus for levitating a magnetic element, theapparatus comprising: means for generating a static magnetic fieldproviding a position-dependent potential energy of interaction with amagnetic element, the static magnetic field providing an equilibriumlocation wherein the potential energy decreases for displacements of themagnetic element away from the equilibrium location along an unstableaxis and increases for displacements of the magnetic element away fromthe equilibrium location in any direction perpendicular to the unstableaxis; means for generating a feedback signal indicative of the locationof the magnetic element on the unstable axis; control means fordirecting the magnetic element to the equilibrium location by providinga quadrupole control magnetic field at the equilibrium location inresponse to the feedback signal.
 38. A method for levitating a magneticelement at an equilibrium location, the method comprising: providing astatic magnetic field providing a position-dependent potential energy ofinteraction with a magnetic element, the static magnetic field providingan equilibrium location wherein the potential energy decreases fordisplacements of the magnetic element away from the equilibrium locationalong an unstable axis and increases for displacements of the magneticelement away from the equilibrium location in any directionperpendicular to the unstable axis; generating a feedback signalindicative of the location of the magnetic element on the unstable axis;forcing the magnetic element toward the equilibrium location byproviding a quadrupole control magnetic field at the equilibriumlocation in response to the feedback signal.
 39. Apparatus forlevitating a magnetic element, the apparatus comprising: at least twomagnets arranged to generate a static magnetic field providing aposition-dependent potential energy of interaction with a magneticelement, the static magnetic field providing an equilibrium locationwherein the potential energy decreases for displacements of the magneticelement away from the equilibrium location along an unstable axis andincreases for displacements of the magnetic element away from theequilibrium location in any direction perpendicular to the unstableaxis, the at least two magnets comprising first and second magnetsspaced apart from one another by a first distance, D1, in a directionparallel to the unstable axis and third and fourth magnets spaced apartfrom one another by a second distance, D2, in a direction perpendicularto the unstable axis, wherein D1<D2 and each of the first and secondmagnets and each of the third and fourth magnets is equidistant from theaxis of symmetry; a position sensor generating a feedback signalindicative of the location of the magnetic element on the unstable axis;and, a controller connected to receive the feedback signal and tocontrol a means for applying a controllable force to the magneticelement to direct the magnetic element to the equilibrium location. 40.Apparatus for levitating a magnetic element, the apparatus comprising:at least two magnets arranged to generate a static magnetic fieldproviding a position-dependent potential energy of interaction with amagnetic element, the static magnetic field providing an equilibriumlocation wherein the potential energy decreases for displacements of themagnetic element away from the equilibrium location along an unstableaxis and increases for displacements of the magnetic element away fromthe equilibrium location in any direction perpendicular to the unstableaxis, the at least two magnets comprising at least two magnetic dipolesspaced apart around a ring, the at least two magnetic dipoles providinga magnetic field component having substantially no gradient at theequilibrium location; a position sensor generating a feedback signalindicative of the location of the magnetic element on the unstable axis;and a controller connected to receive the feedback signal and to controla means for applying a controllable force to the magnetic element todirect the magnetic element to the equilibrium location. 41-42.(canceled)